Junho Yeo

Application of electromagnetic bandgap (EBG) superstrates with controllable defects for a class of patch antennas as spatial angular filters

We present some applications of an electromagnetic bandgap (EBG) superstrate as a spatial angular filter for filtering undesired radiation by sharpening the radiation pattern. Two different defects, one introduced by the ground plane of the antenna and the other produced by a row of defect rods with different dielectric constants in the EBG structure, are simultaneously used as key controllers of directivity enhancement. Initially, we study the unit cell of the EBG structures by varying several parameters, in order to understand how they influence the locations of the bandgap and defect frequencies. Next, the defect frequencies of the unit cell of the EBG cover, and those with high directivity for the EBG antenna composite, are compared to validate the proposed design scheme. Finally, we introduce some interesting applications of EBG superstrates for various types of patch antennas as spatial angular filters, such as a dual-band orthogonally-polarized antenna, a wide-band directive antenna, and an array antenna with grating lobes.

Efficient generation of method of moments matrices using the characteristic function method

We present a new, fast, and efficient technique for computing the MoM matrix elements from Rao-Wilton-Glisson (RWG) bases, one that does not require evaluating the usual surface integrals involving the expansion and testing functions. The matrix elements are represented in terms of characteristic functions (CFs), which can be expressed in a closed canonical form. These universal CFs make matrix generation more efficient and faster than the conventional triangular facet interaction scheme. The proposed technique can be applied for any subsectional basis functions other the RWG if the size of the basis function is small enough compared to the wavelength and the distance between the source and the testing basis functions is beyond a nominal distance. The proposed approach is validated for several canonical geometries, and the accuracy of the generated matrix elements, as well as the radar cross-section (RCS) has been verified.

An algorithm for interpolating the frequency variations of method-of-moments matrices arising in the analysis of planar microstrip structures

This paper presents a new impedance matrix interpolation algorithm, in the context of method of moments, for planar microstrip structures. Three different interpolating functions are implemented depending upon the distance between the basis and testing functions. To demonstrate its efficiency, the technique is applied to several planar microstrip structures, viz. a patch antenna fed by microstrip line and a 4/spl times/4 planar patch array. It is demonstrated that the use of the proposed impedance matrix interpolation scheme can result in significant savings in the computation time with little or no compromise in the accuracy of the solution.

Some novel design for RFID antennas and their performance enhancement with metamaterials

In this presentation we discuss a number of UHF/RFID tag designs including the hybrid loop, dual crossed-dipoles, and the dual crossed-dipoles using an inductively coupled feed. We have carried out extensive parametric studies in the process of analyzing the characteristics of the above antennas, and have investigated several techniques, including meandering, for size-reduction of these antennas. A design methodology based on the genetic algorithm (GA) is presented for the optimization of conformal antennas with electromagnetic bandgap (EBG) surfaces to improve the antenna performance. The EBG characteristic is realized by utilizing a frequency selective surface (FSS) placed above a thin dielectric substrate backed by a metallic ground plane to act as an artificial magnetic conductor (AMC). The antenna is then placed above the EBG surface to create the integrated EBG conformal antenna.

Design of a frequency selective surface (FSS) type superstrate for dual-band directivity enhancement of microstrip patch antennas

A novel design of a high-directivity resonator antenna that utilizes a two-layered frequency selective surface (FSS) superstrate - as an alternative to a dielectric electromagnetic band gap (EBG) superstrate - for dual band directivity enhancement and reduction in height is presented in this paper.

A novel dual-band WLAN antenna for notebook platforms

We present a design for a novel dual-band wireless local area network (WLAN) antenna for notebook platforms. The antenna is a modified inverted-F type antenna printed on a PCB. The radiation patterns of the antenna mounted on several locations of a notebook computer are investigated.

Numerically efficient analysis of microstrip antennas using the Characteristic Basis Function method (CBFM)

This paper presents a novel approach for efficient solution of a class of microstrip antennas using the Characteristic Basis Functions (CBFs) in conjunction with the Method of Moments (MoM), The advantages of applying the CBF method (CBFM) are illustrated with several representative examples, and the accuracy as well as computation times are compared to those of the conventional direct solution to demonstrate the efficiency of CBFM.

Modified Sierpinski gasket patch antenna for multiband applications

In this paper we present an investigation of the Sierpinski gasket patch antenna and propose a novel technique to improve the multiband behavior of this patch antenna.

Investigation of electromagnetic bandgap (EBG) structures for antenna pattern control

In this paper we investigate the use of a variety of EBG structures as components of a number of different antenna designs, with a view to assessing their pattern control capabilities. The EBG configurations investigated include both the one- and two-dimensional geometries comprising of dielectric slabs and rods as well as air pockets in the dielectric. The antenna types used to investigate the EBG materials are microstrip patch, dielectric resonator (DRA) and tapered slot (TSA) types. We compare the numerical simulation results for the gain patterns of original antennas (no EBG) with those that have EBG materials. The studies show that it is not a trivial task to control the radiation characteristics of planar and three-dimensional antennas described in this paper by using EBG structures.

Bandwidth enhancement of multiband antennas using frequency selective surfaces for ground planes

In this paper, a novel approach to improving the bandwidth of multiband antennas using frequency selective surfaces (FSS) is proposed. Numerical simulations of an FSS ground plane that mimics the PMC plane at multiple frequencies are presented.